Empty rule

*{} * {} p {}

ul,
ol {}

Simple rule

p { color: red; }

Important rule

p {
    color: red !important;
    line-height: normal!important;
}
p{position:absolute!important}

@ rule

@media screen and (min-width: 100px) {}

LESS variable

@main-color: red;
.foo {
	background: @main-color;
}

Comment

/* Simple comment here */

String

content: 'foo';

URL

content: url(foo.png);